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Honors Chemistry
Homework Review: Chemical Kinetics
Provide answers on a separate sheet of paper!
1) What units are used to measure reaction rates?
2) Consider the reaction below. How does the rate of F2 consumption compare to the production of NOF?
(Write a mathematical relationship)
2 NO (g) + F2 (g) 2 NOF(g)
3) Consider the reaction mechanism below for the catalyzed destruction of ozone (O3).
Step 1:
Step 2:
4)
5)
6)
7)
Cl + O3 ClO + O2
ClO + O Cl + O2
slow
fast
a. What is the overall reaction?
b. What substance is the reaction intermediate?
c. What substance is the catalyst?
d. Which step is the rate determining step?
How is the rate law of a reaction determined? Is there any other way to determine the rate law of a reaction?
What is the difference between an effective and ineffective collision?
What two factors determine whether a collision is effective?
On the diagram below, label ∆Hrxn, Ea, and where the activated complex exists. Is this reaction endothermic
or exothermic? What is happening to the reactants as the energy rises to the top of the “hill”? What is
happening as the reaction progresses down the hill toward products? Draw a new line to show how the
graph would change if the reaction occurred in the presence of a catalyst.
8) On the diagram below, label ∆Hrxn, Ea, and where the activated complex exists. Is this reaction endothermic
or exothermic? What is happening to the reactants as the energy rises to the top of the “hill”? What is
happening as the reaction progresses down the hill toward products? Draw a new line to show how the
graph would change if the reaction occurred in the presence of a catalyst.
9) What are the five factors that affect the rate of reaction? Describe how each influences the reaction rate.
Answers:
1)
2)
3)
4)
5)
6)
7)
∗ ∗ ∗ ∆ ∆
∆
∆
a. O3 + O 2 O2
b. ClO
c. Cl
d. Step 1
By experiment. NO.
Effective collisions result in a chemical reaction. Inefective collisions do NOT result in a chemical reaction.
Energy of collision, orientation of colliding particles.
This is an endothermic reaction (∆Hrxn > 0). As the reactants gain potential energy and climb the hill, bonds
are being broken. At the top of the “hill” the activated complex exists. As the potential energy decreases
down the hill, energy is being released as the new bonds of the products are formed. Because the reaction is
endothermic, more energy is consumed breaking the reactant bonds than is released as the products bonds
are formed.
8) This is an exothermic reaction (∆Hrxn < 0). As the reactants gain potential energy and climb the hill, bonds
are being broken. At the top of the “hill” the activated complex exists. As the potential energy decreases
down the hill, energy is being released as the new bonds of the products are formed. Because the reaction is
exothermic, more energy is released as the products bonds are formed than is consumed as the reactanct
bonds are broken.
9) Nature of Reactants: Simple, few bonds mean faster reaction rates.
Temperature: Higher temperature, faster reaction rates.
Concentration: Higher concentration, faster reaction rates. (usually)
Surface Area: Higher surface area, faster reaction rates.
Catalyst Present: A catalyst lowers activation energy and increases the reaction rate.